The purpose of this project has been to study the handling of calcium in neurons especially as it involves the endoplasmic reticulum. The approaches taken include: 1) localizaton of Ca-binding sites; 2) attempts to localize Ca stores; 3) using the freeze-fracture techniques to compare structure of junctions between ER and surface membrane of neurons with similar junctions in muscle; 4) studying the appearance of the ER with various conditions known physiologically to alter the amount of Ca in the cytoplasm; 5) correlation of the amount of surface membrane involved in subsurface cistern junctions and the prominance of Ca current during action potentials in various neuronal types; and 6) correlation of a pattern of distribution of subsurface cisterns with bursting membrane potential behavior.